VSC8221 datasheet(29/138 Pages) MICROSEMI

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VSC8221

Data Sheet

VMDS-10106 Revision 4.1

December 2006

29 of 31

10 TWISTED PAIR INTERFACE

The twisted pair interface on the VSC8221 is fully compliant with the iEEE802.3-2000 specification for CAT-5 media. All passive

components necessary to connect the PHY to an external 1:1 transformer have been integrated into the VSC8221. The

connection of the twisted pair interface is shown in the following figure:

Figure 6. Twisted Pair interface

Unlike other Gigabit PHYs, which do not integrate the line terminations in the PHY, the VSC8221’s twisted pair interface is

compatible with a wide variety of standard magnetics and RJ-45 modules from common module vendors. Depending upon the

application (the number of ports, EMi performance requirements such as FCC Class A or B, the type and quality of the

equipment shielding, and other EMi design practices, for example), the twisted pair interface may be used with standard (12- or

8-core) magnetics as well as SimpliPHY’d (4-core) magnetics modules available from many module vendors. in addition, this

interface is also used to provide support for 100Mbps fiber module connection. For more information on the suitability of using

SimpliPHY’d magentics for a particular design, see the Magnetics Guide, available from the Microsemi Web site.

10.1 Twisted Pair Auto-Negotiation (iEEE802.3 Clause 28)

The VSC8221 supports twisted pair auto-negotiation, as defined in iEEE 802.3-2002 clause 28. (However, auto-negotiation is

not defined by iEEE for the 100BASE-FX mode and is therefore not supported.) This process evaluates the advertised

capabilities of the local PHY and its link partner to determine the best possible operating mode. in particular, auto-negotiation

can determine speed, duplex, and MASTER/SLAVE modes for 1000BASE-T. Auto-negotiation also allows the local MAC to

communicate with the Link Partner MAC (via optional “Next-Pages”) to set attributes that may not be defined in the standard. if

the link partner does not support auto-negotiation, the VSC8221 will automatically use parallel-detect to select the appropriate

link speed.

Clause 28 twisted-pair auto-negotiation can be disabled by clearing Mii Register 0.12 – Auto-Negotiation Enable. if auto-

negotiation is disabled, the operating speed and duplex mode of the VSC8221 is determined by the state of Mii Register 0.13,

0.6 – Forced Speed Selection and Mii Register 0.8 – Duplex Mode.

10.2 Twisted Pair Auto MDi/MDi-X Function

For trouble-free configuration and management of Ethernet links, the VSC8221 includes robust Automatic Crossover Detection

functionality for all three speeds on the twisted pair interface (10BASE-T, 100BASE-TX, and 1000BASE-T) – fully compliant with

VSC8221

TXVPA

RJ-45

A+

A-

B+

B-

C+

C-

D+

D-

PHY Port

1000pF, 2kV

0.1µF

TXVNA

TXVPB

TXVNB

TXVPC

TXVNC

TXVPD

TXVND

* SimpliPHY’d magnetics may be used.

For information, refer to the SimpliPHY’d Magnetics

application note.

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